gerheim at cox.net wrote:
> I've been trying to hit PCSAT with a D7. Apparently, the rubber duckie isn't enough wire. Will a telescoping whip do any better?
>> KB9GVR has been having some success.
>> My goal is to send it an APRS packet from a moving motorcycle, so big antennas are out of the question. I almost managed it back in January.
>>>
If you are referring to the OEM duckie that came with the TH-D7, it is
little more than a badly-shielded dummy load. You need something that
is electrically a half-wave design that doesn't depend on a ground plane
as a 1/4-wave whip (even full-sized) does. The problem is that the D7
is simply too small physically to be a significant ground plane (i.e.
counterpoise) to most whips.
I have used a dual-band Maldol replacement whip for the TH-D7 (can't
remember the model number) with great success. This whip is made of
thin, flexible piano wire (non-telescoping) about 20" long . The base
and matching transformer is terminated in an SMA connector for direct
connection to the D7 without the clumsy SMA-to-BNC adapters many people
use. The base of the fitting is flared out so that it contacts an area
on the top panel of the D7 that is about 2 and a half times the radius
of the SMA socket alone which drastically reduces stress and twisting on
the lightweight SMA socket on the radio. This whip radiates about
10-15 dB more RF than the OEM duck (actually measured on an IFR-1500's
spectrum analyzer).
If you are trying to use this for satellite modes, you need to hold the
radio horizontal and at right-angles to the satellite track so that the
dipole-type radiation pattern (max is at right-angles to the whip) will
extend from one horizon to overhead and then down to the other horizon.
--
Stephen H. Smith wa8lmf (at) aol.com
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